2. A tricycle is sitting on a ramp. I place my hand upon the circumference of the front wheel to prevent the tricycle from rolling downhill. I am producing torque, work, and power.

A book I was given at the age of 8 illustrated this in a pair of pictures. A clown on the left is attempting unsuccesfully to lift a chair that is nailed to floor, pulling upwards with all his might. A clown on the right lifts a feather from the floor. The caption, "which clown is doing more work?" At the time the answer seemed most unfair to the chap on the left, but the physics is indisputable. Semantics, on the other hand...

Here we confuse "human effort" with "work". Those steam engine scientists used everyday concepts to explain their engineering,which was all about work getting done,usually moving stuff from one place to another.their analogies break down where there is no movement as such,but it appears some type of work can be done without movement..what about a hard brake into a hairpin from 200km/h...your leg is doing work but nothing is moving.

I am confused by the nature of definition of work. Why must something move for work to be done? Can't work be accomplished without movement? I'm certain I've seen more than one of those people who work without moving be promoted in the past.

In the trim tab idea above, energy is consumed within the electric motor to hold the tab in a particular position. No rotation takes places therefore by strict definition no work is done, but the electrical supply would argue otherwise. Either the definition of work is incomplete or I have a firm misunderstanding of it.

"Work" is a term used to quantify mechanical energy. In the stalled electric motor example, 100% of the electricity is being converted into heat in the motor windings. Conservation of energy principle tells us that the quantity of energy remaining to do useful work is

2. A tricycle is sitting on a ramp. I place my hand upon the circumference of the front wheel to prevent the tricycle from rolling downhill. I am producing torque, work, and power.

A book I was given at the age of 8 illustrated this in a pair of pictures. A clown on the left is attempting unsuccesfully to lift a chair that is nailed to floor, pulling upwards with all his might. A clown on the right lifts a feather from the floor. The caption, "which clown is doing more work?" At the time the answer seemed most unfair to the chap on the left, but the physics is indisputable. Semantics, on the other hand...

Semantics indeed. The analogy is incorrect because the tricycle in not nailed to the floor. It's free to roll down the ramp. Positive work must be constantly applied to maintain the tricycle's position.

More to the point, the book is erroneous in presuming that the intent of mechanical work must always be to move an object some distance. What if the chair is clown physical fitness equipment? Of course we can describe the clown's physical exertion in terms of force, work, power, and energy. We will, however, need something other than a tape measure. We can install load cells in the floor. Meanwhile, we can see that feather-lifting is an inefficient muscular conditioning system, requiring very little *work* from the user.

Imagine a world in which one set of mechanical laws governs conventional bicycles, while another applies to exercise bicycles. I find this inconvenient.

You are only assuming that the work task is rotating a shaft or moving an object some distance. Doesn't have to be, not at all. The work task might be holding an object stationary against an opposing force -- or partially arresting an object moving in the opposite direction. What does a retro-rocket do in a space craft's re-entry? And can we not quantify it in terms of force, work, power, and energy? Of course we can.

Magoo, you are messing practical "achieving a goal" with physics "doing work".

You can burn energy and achieve a goal while holding something still, but that wont produce work on the physics sense. As stated before, work is a measure of force X distance and if there is no distance there is no work or power delivered, period.

What does a retro-rocket do in a space craft's re-entry? And can we not quantify it in terms of force, work, power, and energy? Of course we can.

It's reducing the kinetic energy on the rocket as related to the Earth. You can measure that for sure. It's braking it (or accelerating it backwards by the rocket's own referential). It's raising the universe entropy by releasing waste heat. But then again, it's a force applied to a *MOVING* object.

Semantics indeed. The analogy is incorrect because the tricycle in not nailed to the floor. It's free to roll down the ramp. Positive work must be constantly applied to maintain the tricycle's position.

More to the point, the book is erroneous in presuming that the intent of mechanical work must always be to move an object some distance. What if the chair is clown physical fitness equipment? Of course we can describe the clown's physical exertion in terms of force, work, power, and energy. We will, however, need something other than a tape measure. We can install load cells in the floor. Meanwhile, we can see that feather-lifting is an inefficient muscular conditioning system, requiring very little *work* from the user.

Imagine a world in which one set of mechanical laws governs conventional bicycles, while another applies to exercise bicycles. I find this inconvenient.

You are again mixing achieving a goal with doing work.

And on the stationary bike example, when the rider *ROTATES* the crank delivering torque, he is doing work and power. Because he is moving the crank and inertia wheel.

Canuck, you wrote, I am confused by the nature of definition of work. Why must something move for work to be done? Can't work be accomplished without movement? I'm certain I've seen more than one of those people who work without moving be promoted in the past.

1. Something must move for work to be done because that principle is at the heart of our whole scientific system. It is set by definition going back to the 1820s. Anything defined in cience can also be measured. The measurement of work is a force moving through a distance. For instance, a joule is a newton of force qcting through a meter of distance.

2. A force can be applied to an immovable object and no work can be measured n the object. The person applying the force has work going on internally to his/her body by blood moving, muscles contracting etc but the efficiency of work transformation is zero.

3. Perhaps your non-moving promoted mate was working to the Peter Principle but that is a different branch of science altogether.

Semantics indeed. The analogy is incorrect because the tricycle in not nailed to the floor. It's free to roll down the ramp. Positive work must be constantly applied to maintain the tricycle's position.

Well at that point, in absence of qualifiers that really don't help, I suppose we must agree to disagree. The clowns are right according to conventional physics, and you are wrong, with strawberry sauce. It doesn't matter. Nothing on an interweb talkboard matters. But in the real world you are wrong as well. Hope that helps, lots of love, and grow up.

Let us not forget that work is a specific (mechanical) form of energy- and is IIRC defined as Joe puts it... Work and energy can be dissipated in number of ways, some of them recoverable and some not (e.g. one can use work to heat an object to room temperature by friction, dissipating work into the heat, but that heat will be unrecoverable as long as the object is the same temperature as its surroundings... in order to extract work from it one will have to establish positive temperature differential, e.g. finding a cooler object and using them to power a Stirling engine).

To be a bit pedantic, Joe- I don't think one can measure work... I would think that work can be calculated as energy differential.

Hmmmmm. Does the ladder holding the man 6 feet off the ground perform work? Unless the ladder is a rigid body, it undergoes (hopefully) elastic deformation and changes dimensionally in response to the changes in forces acting upon it as the person climbs it just as the wedge in the tricycle wheel or a nail holding a painting up on the wall. So in any of these examples there is in fact movement, it's just not movement readily apparent to the eye. The object preventing the object from falling is basically a spring that moves until a state of relative stasis is achieved, then moves again when and if the load is removed. Just as a shaft under a twisting force will necessarily deform torsionally. Apply a force to a non-rigid body- i.e. any real world object- and there will be movement. Does a spring perform work as it resists compression or reassumes its uncompressed shape? Or does whatever is deforming the spring perform the work? And does a wind up toy that's been left in a drawer for a year in a wound up state perform work as the catch is released and it goes running across the floor? Or was the work over once the spring was wound?

Re. spring, I think the most correct way of putting it would be that it releases potential energy that was stored in it when it was compressed, usually producing same amount of work that was put into it (minus hysteresis). As for work regarding deformation of non-rigid bodies- I think it's called deformation energy to confuse matters even worse... (mind you, I'm still struggling with Greg's tricycle problem )

So... in real world non ideally rigid bodies, it is apparently literally impossible to apply force without movement resulting. I think the problem then would be the simplifying modelling assumption that there are bodies force can be applied to that are ideally rigid. Angular displacement will never equal zero, no matter how small the force applied.

Canuck, you wrote, I am confused by the nature of definition of work. Why must something move for work to be done? Can't work be accomplished without movement? I'm certain I've seen more than one of those people who work without moving be promoted in the past.

1. Something must move for work to be done because that principle is at the heart of our whole scientific system. It is set by definition going back to the 1820s. Anything defined in cience can also be measured. The measurement of work is a force moving through a distance. For instance, a joule is a newton of force qcting through a meter of distance.

2. A force can be applied to an immovable object and no work can be measured n the object. The person applying the force has work going on internally to his/her body by blood moving, muscles contracting etc but the efficiency of work transformation is zero.

3. Perhaps your non-moving promoted mate was working to the Peter Principle but that is a different branch of science altogether.

Regards

Hey Joe! Long time, no see. Glad you dropped in here. This was only supposed to be a mockery of the Dodge ad but you know how these things go. I've got myself tangled up in semantic it seems and drifted from a discussion of power into work. Seems fairly straight forward though-if I can overcome the output of an electric motor and stall it, then it's no longer generating power(hp) or torque, only force as both of those require motion in the strictest definition.

Well I married a marketing person. And let's just say this: it's better they work on commercials and advertisements than try their hand at science or engineering.

...and the engineers marketing ideas here are you should buy the Dodge because a bicycle will roll down a ramp if you don't hold it,Obama is a commie and a Model T will break your arm if you try to start it wrong.

GG and I said that the "Torque Curve" and the "Power Curve" of an ICE represent the one and same information.

Pay attention to the statements:

Now someone please tell me how you get an engine, attach it to a bench, run it and plot the torque and power curves?

If someone presents me a way to do it other than plotting the toqrue/RPM curve and then multipling it by the RPM to get the power/RPM curve I'll eat my socks.

saudoso,

I'd recommend a nice chianti to accompany your meal of socks marinara. To paraphrase the old joke, "the best way to eat a pair of socks is one bite at a time".

Engineers mostly evaluate recip engine performance in terms of cycle pressures, usually indicated mean effective pressure (IMEP) or brake mean effective pressure (BMEP). The reason torque is commonly used as an indication of engine performance is because it is much less complicated to measure torque on an engine dyno than cycle pressures. Recording cycle pressures requires expensive instrumentation and data acquisition systems.

Getting work out of an engine requires a device to absorb the shaft power, and that is what the dyno "brake" does. The brake or absorber is usually some form of hydraulic pump or electrical generator. The absorber has a load cell that measures the torque reaction produced on it by the engine output. The absorber dissipates the engine power through heat transfer or as electrical power. Torque and power values measured at the dyno brake are defined as "brake horsepower" (BHP) or as "brake torque".

So... in real world non ideally rigid bodies, it is apparently literally impossible to apply force without movement resulting. I think the problem then would be the simplifying modelling assumption that there are bodies force can be applied to that are ideally rigid. Angular displacement will never equal zero, no matter how small the force applied.

So there is always some work done during application of the force or torque to a "real" object courtesy of the movement due to deformation. Once the force stabilises however, we are seeing a real-world case of effort (force) with no work performed.

Magoo is making the classic error of confusing the everyday definition of work with the Newtonian definition where work is a form of energy. Most of us accept that energy cannot be created or destroyed and in examples like the stalled electric motor or the person supporting a weight it can be shown that all the energy being expended is actually appearing as heat in the motor windings or the muscle tissue. So all the energy is accounted for and the object connected to the motor shaft or the mass being supported by the person have clearly not acquired any additional energy, so no work has been performed on either.

A positive displacement in space is not required in order to perform work. It's merely the simplest way to describe it. In the example of the tricycle on the ramp, gravity constantly attempts to roll it downhill, so a continuous force is required to oppose it. From there it's a simple matter to determine the force, work, power, and energy involved in manually holding the tricycle in place versus gravity over an interval of time.

This is not the same case as a man on a ladder because the ladder contributes no energy to the mechanical system. It only presents a vertical force equivalent to mg. But we can make the tricycle akin to the man on the ladder: Instead of applying a torque to the top of the wheel -- or the pedal crank -- to arrest its motion, we can wedge a foot under the wheel. From there we can take off the shoe and walk away barefoot, leaving the tricycle in place. It's not rocket surgery, people.

Someone mention calculus? Total work is simply the time-integral of the instantaneous power applied. Along a trajectory. If any. An ultralight aircraft is capable of 60 mph at max power. Trouble is that in this case, it's flying into a 60 mph headwind. (If you've seen this you know it's fascinating to watch.) Do we suppose that in this case, the poor little aircraft is not producing torque, performing work, and generating power? Of course it is, just the same as if the aircraft were traveling at max speed. Let's not lose our minds here.

You are taking the wrong referential here. Because the aircraft is fighting air resistance and paddling into the air to try to move arround, so the ground has no value as a referential, the air does. So it is infact navigating at 60mph against the head wind all time.

In the example of the tricycle on the ramp, gravity constantly attempts to roll it downhill, so a continuous force is required to oppose it. From there it's a simple matter to determine the force, work, power, and energy involved in manually holding the tricycle in place versus gravity over an interval of time.

The stationary tricycle experiences no change in energy, therefore the work done on the tricycle is zero.

Someone mention calculus? Total work is simply the time-integral of the instantaneous power applied. Along a trajectory. If any. An ultralight aircraft is capable of 60 mph at max power. Trouble is that in this case, it's flying into a 60 mph headwind. (If you've seen this you know it's fascinating to watch.) Do we suppose that in this case, the poor little aircraft is not producing torque, performing work, and generating power? Of course it is, just the same as if the aircraft were traveling at max speed. Let's not lose our minds here.

An aircraft (or any object) moving at constant speed and height is experiencing no nett force so work done on the aircraft is zero. (The thrust provided by the propulsion system is exactly equal to the drag acting in the opposite direction). An energy balance gives the same result, the total energy of the aircraft (kinetic and potential) is not changing so there is no work being done on the aircraft.

There is work being done by the propulsion system - on the air - pushing air backwards behind the aircraft.

The stationary tricycle experiences no change in energy, therefore the work done on the tricycle is zero.

Agreed. If the tricycle had a parking brake on, the effect would be the exact same. The parking brake is indeed applying a force, but no work is getting done and the energy is not changing: it maintains the same potential energy. And the kinetic energy stays at zero, of course.

The tricycle isn't as straight forward as it appears. Just because no work is done on the tricycle itself it doesn't necessarily mean no work will be done.
Think about supporting the tricycle with a small hydraulic cylinder. We could extend the cylinder until the tricycle is positioned where we want it and then release the control valve. The tricycle will then stay there forever, supported by the fluid trapped in the cylinder without any further work being done. We can turn off the pump.
Or we could do it another way, we could crack the control valve just enough to hold the tricycle in place and let the fluid constantly bleed over. No work is being done to the tricycle but we are continually working to maintain the oil pressure and the work is heating the oil.
Manually holding the tricycle is a bit like the second example - no work is being done to the tricycle but energy is being wasted (and work done) simply by maintaining a contracted muscle. Instead of holding it just sit behind it like a human chock. You are still supporting the tricycle, but this time no work is being done (like in the first hydraulic example) and you are free to sleep.

[quote name='Magoo' date='Mar 28 2012, 11:15' post='5633450']
A positive displacement in space is not required in order to perform work. It's merely the simplest way to describe it. In the example of the tricycle on the ramp, gravity constantly attempts to roll it downhill, so a continuous force is required to oppose it. From there it's a simple matter to determine the force, work, power, and energy involved in manually holding the tricycle in place versus gravity over an interval of time.

The fundamentals of physics cannot be evaded by rephrasing words to one's desires which are a state of mind, not relevant to the physical world.

Work is the integral of force acting through a distance. The time duration of a force is not relevant to the amount of work done by that force acting through a distance, and work's units are Ft-Lb force in the English system, or Newton-Meters in the metric system.

The integral of force acting over time is defined as Impulse, the units of which are Lb force-Seconds in the English sytem, and
Newton-Seconds in the metric system. The magnitude of Impulse does not define the amount of work done by a force acting thru a distance.

Yes, but crucially and for clarity, the distance and the force must be in the same direction. Strictly speaking
W=magnitude of force*magnitude of distance it moves *cos(angle between the two vectors)

and for torques W=T*alpha*cos(theta), just for completeness.

In both cases, no motion implies no work being done on the object in question.

Examples using propellers to apply forces to hold things in position are more confusing to think about, but the principle has never been found wanting. Newton's Laws and the work definition apply to all scales of objects at all speeds, whether they are propellers on stationary aircraft, tricycles not moving on hills, atoms, galaxies, electrons.

Even more confusing you can certainly cause work to be done on another system without doing any yourself.

Once you chock the wheel of the tricycle,it is no longer effectively on a downhill ramp.It is as though it is on level ground,and no force is required to keep it from moving. The wheels become mere legs.It is like a brick sitting on a ramp-it will sit there forever.

The thing is you have to discuss which force is zero - there is a force between the chock and the hill and another between the chock and the tricycle, stopping the latter from rolling down the hill.

When chocked the force of gravity is applying ,but no work can be done.Remove the chock,and depending on the steepness of the ramp,some proportion of the force of gravity accelerates the tricycle,the rest of the force of gravity remains as a lessened "weight" of the tricycle. Throw the tricycle off a cliff,it will be weightless and reach it's terminal velocity until..??... hmmm . I'm going out on a limb here and beginning to feel in danger of falling !

The fundamentals of physics cannot be evaded by rephrasing words to one's desires which are a state of mind, not relevant to the physical world.

Right, so please cut it out.

Work is the integral of force acting through a distance. The time duration of a force is not relevant to the amount of work done by that force acting through a distance, and work's units are Ft-Lb force in the English system, or Newton-Meters in the metric system.

The SI unit of work is the joule, which not coincidentally is also an SI unit of energy. One joule is equal to the work required to produce one watt for one second; or, one CV (coulumb volt), which is the work performed in moving an electric charge of one coulomb through an electrical potential difference of one volt.

The integral of force acting over time is defined as Impulse, the units of which are Lb force-Seconds in the English sytem, and Newton-Seconds in the metric system. The magnitude of Impulse does not define the amount of work done by a force acting thru a distance.

Not to be confused with work, the time-integral of instantaneous power.

The thing is you have to discuss which force is zero - there is a force between the chock and the hill and another between the chock and the tricycle, stopping the latter from rolling down the hill.

The key here is that the chock translates no energy to the tricycle.

Now instead of the wheel chock, imagine that you occupy the seat of the tricycle and you are using your feet on the pedals to hold the vehicle in place on the incline. After a minute or two you will start getting tired. After an hour you will be more tired still, and after several hours you will be tired indeed. By this time you may have contrived some means of arranging your foot or leg as a wedge or stop to hold the trike in place so you don't have to do all that work.

Another forum I visit has a similar torque vs. hp thread going at the moment. It's up to 75 pages and still going strong and with no signs of resolution. I'm convinced that these threads are actually an IQ test, but the indicator of intelligence is not to give the "correct" answer but to resist getting sucked into the argument at all.
Clearly I've failed.

Challenging the accepted wisdom of the forum crowd is always good for a thrashing. I tried to point out the lack of correlation between torque and stroke on another board and was summarily tarred and feathered. I have no doubt that even a pair of real-world engines built to demonstrate the point would not be sufficient for the truly invested.

Spending last summer commuting via bicycle, the answer (tq/hp) seems fairly self-explanatory. I'm not sure how anyone who rides a bike could have any other conclusion.